The success of surgical transplantation of organs and tissue is largely dependent on the ability of the clinician to modulate the immune response of the transplant recipient. Specifically, the immunological response directed against the transplanted foreign tissue must be controlled if the tissue is to survive and function. It is known that the normally functioning immune system of the transplant recipient recognizes the transplanted organ as “non-self” tissue and thereafter mounts an immune response to the presence of the transplanted organ. Left unchecked, the immune response will generate a multitude of cells and proteins that will ultimately result in the loss of biological functioning or the death of the transplanted organ.
Transplant rejection remains the leading impediment to long term graft survival in humans. Current immunosuppressive therapy used to treat rejection reactions suppresses T and B cell activity but does not. alter the inflammatory responses that are believed to contribute to transplant rejection (Fryer et al. (1996) Transplantation 62(5)553-559).
Tissue and organ transplant recipients are generally treated with one or more cytotoxic agents in an effort to suppress the transplant recipient's immune response against the transplanted organ or tissue. For example, cyclosporin A (e.g., Neoral® or Sandimmune®), a cyclic peptide consisting of 11 amino acid residues and produced by the fungus species Tolypocladium Inflatum Gams, is currently used to administer to the recipients of kidney, liver, pancreas and heart allografts (i.e., wherein donor and recipient are of the same species). However, administration of cyclosporin A is not without drawbacks as the drug can cause kidney and liver toxicity as well as hypertension. Moreover, the use of cyclosporin A can lead to malignancies (such as lymphoma) and lead to opportunistic infection due to the systemic immunosuppression it induces in patients receiving long term treatment with the drug., i.e., the normal protective immune response of the host to pathogenic microorganisms is downregulated thereby increasing the risk of infections caused by such microorganisms.
Currently available immunosuppressive agents such as cyclosporin A fail to prevent either acute or chronic refractory rejection. Nearly 20% of cadaver kidney and cardiac grafts are lost during the first year post-transplant, primarily due to acute rejection (Uretsky et al. (1987) Circulation 76:827-834; Hosenpud et al. (1994) Transplantation 13:561-570; Canadian Organ Replacement register 1993 report p. 187; Cook et al. (1987) Clinical Transplants 277-285). Chronic rejection poses formidable hurdles for extant immunosuppressant therapies. 50% of lung transplant recipients develop bronchitis obliterans, the hallmark of chronic allograft rejection (Miller, L. (1995) J. Heart Lung Transplant 14:S109-S110; vonWillebrand et al. (1997) Transplantation Proc. 29:1530-1531; Hayry et al. (1996) Transplantation Proc. 28:2337-2338; Tilney et al. (1995) Transplantation Proc. 27:2123-2125; Tilney et al. (1991) Transplantation Proc. 52:389-398). Only 20% of cadaver renal transplants continue to function at ten years post-transplant (Uretsky et al. (1987) Circulation 76:827-834; Hosenpud et al. (1994) Transplantation 13:561-570; Canadian Organ Replacement register 1993 report p. 187; Cook et al. (1987) Clinical Transplants 277-285). Transplant vasculopathy, induced by chronic rejection and ischemia, is the leading cause of cardiac transplant graft loss after the first year post transplant (Miller, L. (1995) J. Heart Lung Transplant 14:S109-S110). Moreover, current post-transplantation therapy requires continuous (e.g. daily) administration of an anti-rejection agent for the duration of the transplant recipient's life.
Although acute rejection is mainly T-cell activated, the role of inflammation has been recently implicated in the pathogenesis of rejection (Hayry et al. (1996) Transplantation Proc. 28:2337-2338). Activation of many cytokines (e.g. IL-2, IFNΥ, TNFα) and chemokines (e.g. RANTES, IL-8, MCP-1 and MIP-1α) occurs during inflammatory responses to graft rejection (Hayry et al. (1997) Transplantation Proc. 29:2551; vonWillebrand et al. (1997) Transplantation Proc. 29:1530-1531; Tilney et al. (1993) 25:861-862). It is believed that decreasing initial inflammation may lead to lower acute and long term rejection rates and improved graft function (Fryer et al. (1996) Transplantation 62(5)553-559).
Chronic rejection is less well understood. Historically, chronic vascular rejection has been described as repetitive endothelial injury leading to intimal proliferation, hypertrophy and subsequent luminal occlusion (Tilney et al. (1995) Transplantation Proc. 27:2123-2125; Tilney et al. (1991) Transplantation Proc. 52:389-398). Some researchers have proposed inflammatory, humoral, cellular, and cytokine-related non-specific scarring mechanisms as etiologies of chronic rejection (Hayry et al. (1996) Transplantation Proc. 28:2337-2338; Tilney et al. (1995) Transplantation Proc. 27:2123-2125; Tilney et al. (1991) Transplantation Proc. 52:389-398). It is now known that alloantigen-independent factors play an essential role in chronic rejection. For example, human kidney grafts from identical twins lose their grafts at ten years (Tilney et al.,(1986) World J. Surgery 10:381-388; Glassock et al. (1968) Medicine 47:411-454). These isograft losses are believed to be a consequence of injury during preservation and reperfusion. Injury from multiple etiologies activates thrombotic and inflammatory cascades in the vascular wall that converge, initiating a rapid pervasive response which stimulates cellular migration, invasion and proliferation at sites of vessel injury (Aziz et al. (1995) Lung Transplant 14:S123-S136; Libby et al., (1992) Circulation 86:Supp:III:47-52). As a result, inflammatory mediators and cytokines are upregulated and secreted in response to endothelial injury, which results in the accumulation of macrophages that, in turn, upregulate more chemokines (e.g. RANTES, IL-8, MCP-1 and MIP-1α) (vonWillebrand et al. (1997) Transplantation Proc. 29:1530-1531), cytokines (e.g. IL-1, IL-6, TNFα) (Tilney et al. (1993) 25:861-862), and growth factors (Hayry et al. (1997) Transplantation Proc. 29:2551).
Large DNA viruses have evolved multiple, highly effective mechanisms over millions of years which enhance or inhibit the thrombotic/thrombolytic and inflammatory cascades and alter cellular invasion into areas of tissue injury (Gooding, et al. (1992) Cell, 667:141-150; Spriggs, M. K. (1996) Annu. Rev. Immunol, 14:101-130; Smith G. L. (1994) Trends Microbiol., 82:80-88). Both the thrombotic/thrombolytic serine proteinases and the inflammatory cytokine cascades have been recently demonstrated to stimulate cellular chemotaxis and mitogenesis (Blasi, F (1997) Trends in Immunol. Today, 18:415-419; Luster, A. D. (1998) N. End. Journal, 338: 436-445). The proteins secreted by myxoma virus frequently. mimic cellular immune molecules such as cytokine receptors and function by binding and inhibiting cytokines and chemokines or other regulatory proteins (McFadden, et al. (1995) Leukocvte Biol., 57:731-738; Mossman, et al. (1995) J. Biol. Chem., 270:3031-3038). We have previously reported that Serp-1, a serine proteinase inhibitor, inhibits inflammation and atheroma development in rabbit and rat models after balloon injury and dramatically reduces macrophage invasion and atherosclerotic plaque growth in cholesterol fed rabbits after angioplasty injury (Lucas, et al. (1996) Circulation, 94:2890-2900). Preliminary studies in a rat aortic allograft model have also demonstrated significant reductions both in mononuclear cell invasion and transplant vasculopathy after infusion of these viral proteins (Miller, et al. (2000) Circulation, 101: 1598-1605; Mossman, et al. (1996) Virology, 215: 17-30).
Serp-1 is a 55kD glycoprotein that inhibits a variety of serine proteinases that regulate the inflammatory response. Serp-1 regulates thrombolytic proteins, plasmin, tissue plasminogen activator (tPA) and urokinase. A single local infusion of Serp-1 protein, cloned and expressed from a vaccinia vector, at the site of balloon injury dramatically decreases subsequent plaque growth and macrophage invasion (Lucas, et al. (1996) supra). Serp-1 modulates transcription of elements of the thrombolytic cascade soon after endothelial injury. Serp-1 is the subject of three U.S. Pat. No. 5,686,409, entitled “Antirestenosis Protein”; and U.S. Pat. Nos. 5,919,014 and 5,939,525 both entitled “Methods of Treating Inflammation and Compositions Therefor.”
It has been discovered in accordance with the present invention that co-administration of Serp-1, Serp-1 analogs and biologically active fragments thereof and an anti-rejection agent are capable of preventing allograft and xenograft transplant rejection in mammals without the need for sustained administration of an anti-rejection agent.